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UNIVERSITY  OF  ILLINOIS 

AT  URBANA-CHAMPAICN 


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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  258 


EXPERIMENTS  WITH  SUBSOILING, 
DEEP  TILLING,  AND  SUBSOIL 
DYNAMITING  ; 

BY  RAYMOND  S.  SMITH 

THE  UBRARY  OF  THE 

MAR  28 1925 

UNIVEKSIIY  vt  ILLINOIS 


URBANA,  IT.TJNOIS,  FEBRUARY,  1925 


SUMMARY 

Deep  plowing  and  subsoil  dynamiting  experiments  in 
Illinois  as  well  as  in  other  states  indicate  that  these  tillage 
methods  cannot  be  expected  materially  to  increase  crop  yields. 
That  such  methods  are  not  superior  to  ordinary  or  medium- 
depth  plowing  has  been  indicated  by  subsoiling  experiments 
conducted  by  the  Illinois  Agricultural  Experiment  Station  on 
Gray  Silt  Loam  On  Tight  Clay  at  Odin,  Marion  county; 
subsoiling,  deep  tilling,  and  dynamiting  experiments  on  Gray 
Silt  Loam  On  Tight  Clay  at  Toledo,  Cumberland  county; 
and  deep  tilling  experiments  on  Brown  Silt  Loam  at  Urbana, 
Champaign  county. 

Soil  moisture  determinations  made  during  two  seasons 
on  the  variously  tilled  plots  at  Toledo  show  that  none  of  the 
tillage  treatments  used  increased  the  downward  movement 
of  moisture  thru  the  soil. 


EXPERIMENTS  WITH  SUBSOILING,  DEEP 
TILLING,  AND  SUBSOIL  DYNAMITING 

By  RAYMOND  S.  SMITH,  Associate  Chief  in  Soil  Physics 

Good  plowing  is  often  taken  to  mean  deep  plowing.  The  two,  how- 
ever, are  not  associated,  and  before  a  farmer  decides  to  increase  the 
depth  of  plowing  beyond  about  7  inches,  he  should  consider  whether  the 
probable  benefits  will  more  than  pay  for  the  increased  cost. 

The  purpose  of  plowing  is  to  turn  under  organic  matter  of  various 
kinds,  to  pulverize  the  surface  so  that  the  seed  may  be  covered  at  the 
right  depth,  to  control  weeds,  and  to  check  surface  runoff.  In  heavy 
soils,  or  soils  which  pack  badly  after  rains,  plowing  is  effective  in  help- 
ing to  maintain  a  favorable  physical  condition.  Plowing  does  not  increase 
the  water-holding  capacity  of  the  soil,  even  in  arid  regions;  it  does, 
however,  increase  the  power  of  the  soil  to  absorb  rainfall,  thus  decreas- 
ing the  amount  of  water  carried  away  by  surface  runoff. 

The  supposed  desirability  of  deep  plowing  seems  to  be  based  on  the 
belief  that  only  the  portion  of  the  soil  which  is  loosened  by  the  plow  is 
utilized  by  the  roots  of  the  crop.  There  are  no  reasons  for  believing 
that  the  roots  of  crop  plants  behave  in  any  way  essentially  different 
from  the  roots  of  wild  plants,  and  the  luxuriant  growth  of  wild  vegeta- 
tion on  land  which  has  never  been  plowed  is  a  matter  of  common 
knowledge. 

There  are  soils,  however,  which  are  unfavorable  to  root  penetration 
because  they  have  an  impervious  subsoil,  and  it  would  be  very  desirable 
to  overcome  this  condition.  Whether  this  can  be  done  by  deep  tillage 
of  any  kind  will  be  discussed  later. 

The  increased  cost  of  deep  plowing  is  considerable.  If  the  depth 
is  increased  one  inch,  about  300,000  pounds,  or  150  tons,  of  additional 
soil  is  turned  for  every  acre  plowed.  This  additional  weight  cannot  be 
moved  without  expenditure  of  additional  power,  and  power  on  the 
farm  is  costly. 

In  this  bulletin  the  terms  shallow,  medium,  and  deep  plowing  are 
used  with  the  following  meanings: 

Shallow  plowing,  less  than  5  inches  deep 
Medium  plowing,  between  5  and  8  inches 
Deep  plowing,  more  than  8  inches  deep 

The  only  way  to  determine,  with  any  degree  of  accuracy,  how  deep 
the  plow  is  running  is  to  make  several  careful  measurements.  It  is  almost 

155 


156 


BULLETIN  No.  258 


[February, 


always  true  that  the  plowman  thinks   he  is  plowing  deeper  than  he 
actually  is. 

The  subject  of  depth  of  plowing  is  of  such  general  interest  that  a 
few  of  the  experiments  which  have  been  conducted  in  other  states,  and 
all  the  Illinois  experiments  will  be  presented  in  this  bulletin  so  that  the 
reader  may  see  whether  there  is  any  basis  for  the  expectation  that  deep 
plowing  will  increase  yields. 

PLOWING  EXPERIMENTS  IN  OTHER  STATES 

In  1918  Chilcott  and  Cole,1  of  the  Bureau  of  Plant  Industry  of  the 
United  States  Department  of  Agriculture,  reported  the  results  of  exten- 
sive deep  tillage  work  in  the  Great  Plains  which  had  been  carried  on 
for  a  period  of  years  at  twelve  stations  in  nine  states.  The  authors  con- 
cluded that  the  "average  results  of  a  series  of  years  show  no  measurable 
effect  on  crop  yields  as  a  result  of  subsoiling." 

Results  obtained  by  the  Ohio  Agricultural  Experiment  Station 
from  experiments  comparing  ordinary  plowing,  deep  plowing,  and  sub- 
soiling,  are  summarized  in  Table  1.  The  authors  comment  on  these 
results  as  follows :  "It  would  be  difficult  to  arrange  a  uniform  treatment 
which  would  result  in  yields  more  nearly  identical.  In  view  of  the  ex- 
pense involved,  it  is  evident  that  the  7-inch  plowing  is  by  far  the  most 
profitable." 


TABLE   1.— AVERAGE  YIELDS   PER  ACRE  FOR  TWELVE  YEARS  FOLLOWING  DIFFERENT 

DEPTHS  OF  PLOWING 

(From  Ohio  Agricultural  Experiment  Station  Bulletin  362) 


Crop 

Ordinary  plowing 
(7#  inches) 

Deep  plowing 
(15  inches) 

Ordinary  plowing 
plus  subsoiling 

Grain 

Straw  or 
hay 

Grain 

Straw  or 
hay 

Grain 

Straw  or 
hay 

Corn  

bu. 
61.13 
49.00 
31.50 

Ibs. 
3  251 
2  159 
3  483 
5  300 

bu. 
59.47 
49.29 
31.49 

Ibs. 
3  066 
2  048 
3  517 
5  060 

bu. 
61.33 
49.05 
31.65 

Ibs. 
3  229 
2  188 
3  549 
5  200 

Oats  

Wheat  

Clover  

Noll,1  of  the  Pennsylvania  Agricultural  Experiment  Station,  reports 
several  years'  work  comparing  the  effect  of  ordinary  plowing  (7  inches) 
and  deep  plowing  (12  inches),  on  the  yields  of  corn,  oats,  barley,  wheat, 
and  alfalfa.  He  was  led  to  conclude  that  "the  two  kinds  of  plowing  gave 
practically  the  same  results  on  all  crops  grown."  Since  the  results  with 
alfalfa  are  of  special  interest,  they  are  given  in  Table  2. 


Chilcott,  E.  C.,  and  Cole,  John  S.   Subsoiling,  deep  tilling,  and  soil  dynamiting  in 
the  Great  Plains.   Jour.  Agr.  Res.    14:481-521,  1918. 


.7925]  SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING  157 

Numerous  other  experiments  on  depth  of  plowing,  conducted  under 
a  wide  range  of  climatic  and  soil  conditions  in  many  states,  all  lead  to 
the  conclusion  that,  while  occasionally  a  combination  of  soil  and  climatic 

TABLE  2. — YIELD  OF  ALFALFA  FROM  SHALLOW  AND  FROM  DEEP-PLOWED  PLOTS* 
(From  Pennsylvania  Agricultural  Experiment  Station  Annual  Report,  1912-1913) 


Shallow-plowed 
plots 

Deep-plowed 
plots 

First  cutting  

Ibs. 
1  768 

Ibs. 
1  725 

Third  cutting  

871 

827 

*Second  cutting  not  harvested  because  it  was  too  light  owing  to  drouth. 

conditions  may  occur  which  makes  deep  plowing  profitable,  the  returns 
thru  a  period  of  years  will  not  justify  the  increased  cost,  excepting  pos- 
sibly in  the  case  of  sugar  beets. 

SUBSOIL  DYNAMITING  EXPERIMENTS  IN 
OTHER  STATES 

The  use  of  dynamite  on  soils  having  an  impervious  subsoil  is 
strongly  recommended  by  concerns  having  this  material  for  sale.  The 
fact  that  the  character  of  the  impervious  material  determines  whether 
or  not  dynamite  can  be  used  beneficially  seems  to  have  been  overlooked 
by  them  in  their  advertising.  The  effect  of  the  exploding  charge  on  a 
plastic  clay  subsoil  is  injurious  rather  than  beneficial  because  the  clay 
is  compacted  and  not  shattered.  The  accompanying  illustration  from 
Bulletin  209  of  the  Kansas  Agricultural  Experiment  Station  (Fig.  1) 
shows  the  effect  produced  by  exploding  a  charge  of  dynamite  in  such  a 
subsoil.  The  soil  particles  are  forced  out  from  the  center  of  the  charge 
and  into  the  pore  spaces  of  the  surrounding  soil  mass,  forming  dense 
walls.  These  walls  are  very  strongly  compacted  and  may  be  easily  sep- 
arated from  the  adjacent  soil,  as  was  done  in  this  Kansas  work.  Pro- 
fessors Call  and  Throckmorton  comment  as  follows  on  the  effect  of 
dynamiting  plastic  clay  subsoils:  "It  is  evident  from  these  observations 
that  dynamiting  does  not  crack  and  loosen  plastic  clay  subsoils.  In 
fact,  the  opposite  effect  is  produced.  The  soil,  instead  of  being  shattered 
and  cracked,  is  compacted  and  puddled,  and  the  soil  left  in  poorer  physi- 
cal condition  than  before  the  dynamiting  was  done."  Similar  effects 
were  noted  in  the  dynamiting  experiments  at  Toledo,  Illinois,  which  are 
discussed  beginning  on  page  r&l.  A  number  of  other  states  have 
conducted  subsoil  dynamiting  experiments  and  the  results  of  practically 


C.  F.    Pennsylvania  Agricultural  Experiment  Station  Annual  Report,   1912- 
1913. 


158  BULLETIN  No.  258  [February, 


FIG.  1. — A  PARTLY  BROKEN  DYNAMITE  JUG  IN  A  HEAVY  PLASTIC  SUBSOIL 

Produced  by  one-half  stick  of  20-percent  "Red  Cross"  powder  placed  in  the 
soil  at  a  depth  of  three  feet.  Cavity  twelve  inches  wide  and  fifteen  inches  deep; 
thickness  of  walls  varied  from  two  to  six  inches.  "The  soil,  instead  of  being  shat- 
tered and  cracked,  is  compacted  and  puddled,  and  left  in  poorer  physical  condition 
than  before  the  dynamiting  was  done."  (Courtesy  of  the  Kansas  Agricultural 
Experiment  Station.) 

all  of  these  experiments  lead  to  the  conclusion  that  for  general  farm 
crops  as  well  as  for  fruit  trees,  the  effect  of  dynamiting  plastic  subsoils 
is  injurious  rather  than  beneficial. 

PLOWING  EXPERIMENTS  IN  ILLINOIS 

Considerable  work  has  been  done  in  Illinois  in  comparing  the 
effects  of  medium  and  deep  plowing,  as  already  defined,  on  crop  yields. 
The  following  experiments,  all  of  which  have  been  discontinued,  include 
all  the  plowing  studies  made  by  this  Station,  excepting  some  early  work 
with  sugar  beets,  the  results  of  which  were  published  in  1898  in  Bul- 
letin 49. 

EXPERIMENT  AT  ODIN  :   GRAY  SILT  LOAM  ON  TIG'HT  CLAY 

From  1907  to  1919  a  subsoiling  experiment  was  carried  on  at  the 
Odin  experiment  field,  in  Marion  county.  The  soil  on  this  field  is  classi- 
fied as  Gray  Silt  Loam  On  Tight  Clay.  The  plastic,  difficultly  pervious 
stratum  known  as  "tight  clay"  is  from  8  to  12  inches  thick  and  generally 
occurs  about  19  inches  below  the  surface,  tho  there  is  a  great  variation 
in  its  depth.  In  some  places  it  comes  very  close  to  the  surface,  and  gives 
rise  to  what  are  known  as  "scald  spots." 


SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING 


159 


TABLE  3. — ACRE  YIELDS  OF  CORN  GROWN  ON  GRAY  SILT  LOAM  ON  TIGHT  CLAY,  NOT 
TILE-DRAINED:    ODIN  FIELD 


Plot  

1 

2 

3 

4 

5 

Soil  treatment1 

None 

R 

RL 

RLP 

RLPK 

Tillage 
treatment  .  . 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

19072... 

bu. 
50.3 
42.2 
28.6 
32.8 
22.8 
28.2 
-3.8 
5.2 
48.6 
17.6 
7.4 
2.8 
0.8 

bu. 

7.3 
36.4 
27.2 
17.9 
19.6 
32.2 
3.6 
2.8 
38.8 
14.0 
9.4 
6.0 
0.3 

bu. 

49.9 
37.8 
32.8 
26.5 
22.6 
40.8 
6.0 
2.0 
46.0 
16.2 
12.7 
6.8 
1.2 

bu. 
38.9 
24.8 
29.8 
31.4 
24.4 

bu. 
41.8 
34.6 
27.8 
38.0 
21.6 

bu. 
48.8 
31.4 
26.8 
37.8 
23^0- 
A4.2 
11.2 
1.8 
46.4 
23.4 
8.0 
9.0 
4.1 

bu. 
48.6 
40.4 
36.2 
36.6 
21.8 
41.2 
5.0 
2.0 
44.8 
20.6 
7.0 
10.4 
2.2 

bu. 

42.8 
45.8 
34.2 
36.5 
20.6 
52.0 
3.6 
2.8 
42.0 
22.2 
12.0 
9.6 
2.1 

bu. 

70.8 
75.0 
71.8 
76.7 
39.2 
68.8 
11.6 
2.8 
61.2 
28.0 
34.6 
17.2 
2.8 

bu. 
63.5 

57.8 
66.4 
85.4 
47.6 
57.2 
11.8 
5.2 
55.2 
23.4 
32.8 
18.2 
1.9 

19082  

1909     . 

1910  

1911  

1912s...  . 

14*3* 
4.8 
3.8 

48.2 
19.8 
7.7 
5.6 
0.7 

sP7z" 

4.2 
1.8 
46.2 
22.2 
7.0 
8.8 
4.0 

19132  

19142  

19152  

19162  

1917  

19182  

1919  

Average  .  . 

23.7 

19.7 

23.2 

19.6 

23.3 

23.8 

24.4 

25.1 

43.1 

40.5 

*R  =  residues,  L  =  lime,  P  =  rock  phosphate,  K  =  kainit. 

2Replowed  in  spring. 

'Plowed  and  subsoiled  in  spring. 


TABLE  4. — ACRE  YIELDS  OF  CORN  GROWN  ON  GRAY  SILT  LOAM  ON  TIGHT  CLAY,  TILE- 
DRAINED:    ODIN  FIELD 


Plot  

6 

7 

8 

9 

10 

Soil  treatment 

None 

R 

RL 

RLP 

RLPK 

Tillage 
treatment  .  . 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

19071  

bu. 
38.5 
28.8 
30.0 
24.9 
10.8 
24.0 
1.2 
3.4 
22.0 
9.2 
11.1 
5.6 
0.1 

bu. 
27.9 
28.6 
21.0 
27.2 
7.0 
31.2 
2.8 
5.2 
24.6 
10.8 
9.7 
6.0 
0.3 

bu. 
50.3 
28.6 
28.0 
39.1 
15.4 
38.4 
1.8 
4.6 
35.0 
15.2 
15.4 
8.0 
0.2 

bu. 
47.4 
28.0 
24.6 
38.8 
15.4 
33.2 
2.4 
4.8 
38.4 
13.2 
12.8 
7.0 
0.2 

bu. 
52.8 
36.4 
30.6 
42.6 
27.8 
53.0 
4.0 
2.4 
49.0 
16.8 
15.4 
14.2 
1.6 

**. 

45.8 
38.4 
30.2 
37.3 
22.4 
50.8 
4.0 
3.0 
41.6 
18.6 
15.7 
13.6 
1.8 

bu. 
45.3 
39.4 
21.6 
40.8 
23.8 
57.6 
7.2 
2.0 
41.6 
18.4 
20.6 
15.2 
1.5 

bu. 

45.9 
46.0 
41.0 
43.2 
19.2 
54.2 
12.2 
2.2 
41.8 
17.6 
15.6 
15.8 
2.4 

bu. 
69.4 

77.2 
36.2 
83.0 
32.2 
62.0 
8.6 
3.4 
53.6 
35.8 
27.2 
22.4 
4.2 

**. 

55.3 
62.8 
54.4 
85.9 
33.2 
39.8 
8.6 
4.8 
44.8 
30.6 
27.6 
21.2 
4.6 

19081  

1909  

1910  

1911  

19122  

19131  

19141  

19151  

19161  

1917  

19181  

1919  

Average  

16.1 

15.6 

21.5 

20.5 

26.2 

24.9 

25.7 

27.5 

39.6 

36.4 

1Replowed  in  spring. 

"Plowed  and  subsoiled  in  spring. 


160 


BULLETIN  No.  258 


[February, 


TABLE  5. — SUMMARY  OF  ACRE  YIELDS  OF  CORN  FROM  TILED  PLOTS  AND  FROM  PLOTS 

NOT  TILED:    ODIN  FIELD 


Soil  treatment 

None 

R 

RL 

RLP 

RLPK 

Tillage 
treatment  .  . 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

Not 
sub- 
soiled 

Sub- 
soiled 

19071  

bu. 
44.4 
35.5 
29.3 
28.9 
16.8 
26.1 
2.5 
4.3 
35.3 
13.4 
9.3 
4.2 
0.5 

bu. 
37.6 
32.5 
24.1 
22.5 
13.3 
31.7 
3.2 
4.0 
31.7 
12.4 
9.5 
6.0 
0.3 

bu. 
50.1 
33.2 
30.4 
32.8 
19.0 
39.6 
3.9 
3.3 
40.5 
15.7 
14.1 
7.4 
0.7 

bu. 
43.2 
26.4 
27.2 
35.1 
19.9 
24.0 
3.6 
4.3 
43.3 
16.5 
10.3 
6.3 
0.4 

bu. 

47.3 
35.5 
29.2 
40.3 
24.7 
48.6 
4.1 
2.1 
47.6 
19.5 
11.2 
11.5 
2.8 

bu. 

47.3 
34.9 
28.5 
37.5 
22.7 
47.5 
4.1 
2.4 
44.0 
21.0 
11.8 
11.3 
3.0 

bu. 
47.0 
39.9 
28.9 
38.7 
22.8 
49.4 
6.1 
2.0 
43.2 
19.5 
13.8 
12.8 
1.9 

bu. 
44.4 
45.9 
37.6 
39.9 
19.9 
53.1 
7.9 
2.5 
41.9 
19.9 
13.8 
12.7 
2.3 

bu. 
70.1 
76.1 
54.0 
79.9 
35.7 
65.4 
10.1 
3.1 
57.4 
31.9 
30.9 
19.8 
3.5 

bu. 
59.4 
60.3 
60.4 
85.7 
40.4 
48.5 
10.2 
5.0 
50.0 
27.0 
30.2 
19.7 
3.3 

19081          .    .  . 

1909  

1910     

1911 

19122 

19131  

19141  

19151  

19161  

1917  

19181  

1919     

Average  .  . 

19.9 

17.7 

22.3 

20.0 

24.7 

24.3 

25.0 

26.3 

41.3 

38.4 

Treatment 


None 


Le 


LeL 


LeLP 


LeLPK 


Odin  Summary  of  Corn  Yields 

Bushels  per  acre 

5        10        IS       20       25      30       35       40 


^eplowed  in  spring.         "Plowed  and  subsoiled  in  spring. 

During  this  13-year  period  the  rotation  used  was  corn,  soybeans, 
wheat,  and  clover.  There  were  four  failures  of  the  corn  crop,  three  poor 
corn  crops,  four  poor  wheat  crops,  and  twelve  clover  failures.  The  large 
proportion  of  crop  failures  which  occurred  in  spite  of  supposedly  good 
soil  treatment  makes  it  clear  that  crops  on  this  soil  type  are  very  sensi- 
tive to  climatic  conditions  during  the  growing  season.  It  was  the  appre- 
ciation of  this  fact  that  led 
to  the  starting  of  the  sub- 
soiling  work,  in  an  attempt 
to  determine  whether  such 
tillage  treatment  would  im- 
prove the  unfavorable  sub- 
soil condition.  It  should  be 
stated,  however,  that  when 
seasonal  conditions  are  fa- 
vorable, large  crops  can  be 
grown  on  this  soil  if  it  is 
properly  treated. 

One-half  of  each  plot  was 
plowed  and  subsoiled  in  the 
late  fall.  Exceptions  to  this 
procedure  are  noted  in  foot- 
notes following  Tables  3 
and  4.  The  yields  of  the 
crops  other  than  corn  are 
omitted  because  they  were 


FIG.    2. — SLIGHT    VARIATIONS    INDICATE    THAT 
SUBSOILING  HAS  No  EFFECT  ON  CORN  YIELDS 


1925~\ 


SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING 


161 


not  harvested  by  half  plots.  The  complete  data  for  corn  given  in  Tables 
3  and  4  show  the  variations  which  enter  into  the  averages  given  in  the 
summary,  Table  5. 

In  every  case  the  differences  in  yield  between  the  subsoiled  plots 
and  the  plots  not  subsoiled  are  so  small  that  the  only  possible  conclusion 
is  that  subsoiling  has  neither  increased  nor  decreased  the  corn  yields. 

The  averages  given  in  Table  5  are  shown  in  graphic  form  in  Fig.  2. 

EXPERIMENT  AT  TOLEDO:    GRAY  SILT  LOAM  ON  TIGHT  CLAY 

In  1913  another  experiment  was  started  on  Gray  Silt  Loam  On 
Tight  Clay  at  Toledo,  Cumberland  county,  to  compare  the  effects  of 
subsoiling,  deep  tillage,  and  subsoil  dynamiting  with  ordinary  plowing, 
in  a  rotation  of  corn,  soybeans,  wheat,  and  sweet  clover.  Four  series  of 
four  1/10-acre  plots  each  were  laid  out  so  that  each  crop  was  grown 
each  year.  The  second-year  sweet  clover  stubble  was  plowed  late  in 


FIG.  3. — DEEP  TILLAGE  MACHINE.    REAR  DISK  TURNS  THE  SOIL  IN  THE  BOTTOM 
OF  FURROW  MADE  BY  FRONT  DISK 

This  machine  mixed  the  subsurface  and  in  places  the  subsoil  with  the  surface  soil 
to  such  an  extent  as  to  change  the  color  of  the  surface.  Decreased  yields  were  appar- 
ently the  result  of  this  mixing. 


the  fall  for  corn.  One  ton  of  rock  phosphate  per  acre  was  applied  on  all 
plots  in  the  fall  of  1914,  and  again  in  the  fall  of  1918.  Four  tons  of 
limestone  per  acre  was  applied  on  all  plots  in  1913,  three  tons  per  acre 
was  applied  for  the  1917  crop,  and  two  tons  per  acre  for  the  1921  crop. 
The  depth  from  the  surface  to  the  tight  clay  varies  on  this  field, 
as  is  always  found  to  be  the  case  with  this  soil  type.  In  places,  the 


162 


BULLETIN  No.  258 


[February, 


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.7925]  SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING  163 

subsoil  plow  and  deep  tillage  machine  penetrated  the  tight  clay,  but  as 
a  rule  this  impervious  stratum  occurred  1  to  16  inches  below  the  depth 
to  which  the  implements  ran.  The  deep  tilling  was  done  with  a  deep 
tillage  machine,  illustrated  in  Fig.  3,  which  mixed  the  subsurface,  and  in 
places  the  subsoil,  with  the  surface  soil  to  such  an  extent  as  to  change 
the  color  of  the  surface.  On  the  dynamite  plots,  the  charge  was  placed 
well  into  the  tight  clay  stratum.  The  size  of  the  charge  was  determined 
each  year  by  experimentation,  the  object  being  to  use  as  heavy  a  charge 
as  possible  without  blowing  the  soil  out  and  forming  a  hole.  The  charges 
usually  consisted  of  one-third  of  a  stick  of  20-percent  dynamite.  They 
were  spaced  8  feet,  3  inches  apart  each  way  on  two  of  the  plots  and  1 1 
feet  apart  each  way  on  the  other  two.  Fig.  4  shows  the  method  used 
in  spacing  the  charges. 

The  results  of  this  experiment  show  that  none  of  the  tillage  treat- 
ments— subsoiling,  deep  tilling,  or  dynamiting — had  any  beneficial  effect 
on  crop  yields.  Deep  tilling  apparently  decreased  yields,  probably  be- 
cause of  the  mixing  of  the  subsurface  and  subsoil  with  the  surface  soil. 

Table  6  shows  the  yields  of  all  the  crops  during  the  time  of  the 
experiment,  1913  to  1922,  and  also  the  time  when  the  various  series 
were  plowed,  subsoiled,  deep-tilled,  and  dynamited.  It  should  be  ex- 
plained that  the  tilling  was  done  in  the  late  fall  of  the  year  indicated, 
for  the  following  corn  crop. 

In  Table  7  the  results  of  the  Toledo  experiment  are  summarized. 

TABLE  7. — SUMMARY  OF  CROP  YIELDS:    TOLEDO  FIELD 
(Bushels  per  acre) 


Tillage 
treatment 

Corn 
9  crops 

Soybeans 

7  crops 
1 

Wheat 
6  crops 

Sweet  clover 
seed 
6  crops 

Plowed  7  in 
Subsoiled  1 
Deep  tilled 
Dynamited 

ches  deep  

40.2 
41.9 
37.4 
40.3 

16.3 
16.2 
15.2 
16.4 

13.5 
12.9 
10.8 
11.7 

3.68 
3.65 
3.18 
4.25 

i  inches  deep  

14  inches  

SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING  FAIL  TO  OPEN 
UP  TIGHT  CLAY  SUBSOIL 

The  fundamental  cause  of  the  frequent  crop  failures,  low  yields, 
and  relatively  low  agricultural  value  of  Gray  Silt  Loam  On  Tight  Clay 
is  the  presence  of  the  tight  clay  subsoil.  In  the  spring  the  soil  is  super- 
saturated. The  surplus  water  which  cannot  be  removed  by  surface 
drainage  remains  until  removed  by  evaporation.  This  condition  results 
in  poor  root  growth  and  the  crops  are  very  sensitive  to  the  dry,  hot 
weather  which  commonly  follows  the  spring  rains. 


164 


BULLETIN  No.  258 


[February, 


PLOTS  4  and  8 
Charges    8' -3"  by   8 '-3' 

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PLOTS    12  and   16 
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FIG.  4. — METHOD  OF  SPACING  CHARGES  ON  DYNAMITED  PLOTS 

The  charge  was  placed  well  into  the  tight  clay  stratum  and  made   as  heavy  as 
possible  without  being  so  heavy  as  to  blow  the  soil  out  and  form  a  hole. 


.  19251  SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING  165 

That  a  solution  of  this  problem  is  not  to  be  found  in  subsoiling, 
deep  tilling,  or  dynamiting  is  indicated  by  the  results  of  these  experi-, 
ments.  Any  such  treatment  to  be  effective  would  have  to  shatter  or 
open  up  this  impervious  stratum  sufficiently  to  increase  the  passage  of 
water  thru  it  and  to  allow  roots  to  penetrate  it  readily.  The  character 
of  the  material  is  such  that  it  is  rarely,  if  ever,  dry  enough  to  be  shat- 
tered, and  it  seems  very  unlikely  that  it  would  remain  shattered  any 
length  of  time  even  if  such  a  condition  could  be  produced. 


FIG.  5. — DEPRESSION  FOUND  IN  THE  SPRING  OVER  EACH  SPOT  WHERE  A 
CHARGE  OF  DYNAMITE  WAS  EXPLODED  THE  PREVIOUS  FALL 

These  basins  were  entirely  impervious  to  water.   A  subsoil  that  is 
plastic  in  nature  cannot  be  opened  up  successfully  with  dynamite. 

The  dynamite  charges,  instead  of  shattering  the  tight  "clay,  formed 
perfect  basins  with  highly  compacted  walls  which  were  entirely  imper- 
vious to  water.  In  the  spring,  the  location  of  every  charge  of  the  pre- 
vious fall  was  indicated  by  a  small  depression.  (See  Fig.  5.)  It  appears 
to  be  a  universal  rule  that  dynamite  cannot  be  used  successfully  to  open 
up  a  subsoil  which  is  plastic  in  nature. 

The  term  "hardpan"  is  commonly  applied  to  the  tight  clay  stratum; 
however,  it  is  very  different  from  true  hardpan.  True  hardpan  is  not 
known  to  occur  in  Illinois.  It  is  a  cemented  stratum  common  in  semi- 
arid  regions  and  it  can  be  broken  up  successfully  with  dynamite.  Tight 
clay  is  not  a  cemented  layer;  instead,  it  is  very  plastic,  due  to  its  high 
percentage  of  very  fine  particles.  The  effect  of  the  dynamite  charges  on 
the  plastic  clay  was  harmful,  rather  than  beneficial,  as  is  shown  in  Fig.  6, 
and  as  was  shown  in  the  Kansas-  work. 


166 


BULLETIN  No.  258 


[February,. 


In  order  to  get  further  evidence  as  to  whether  the  subsoiling,  deep 
tilling,  or  dynamiting  had  any  effect  on  the  passage  of  moisture  thru 
the  tight  clay  stratum,  samples  were  taken  in  the  spring  of  1919  and  of 
1920  for  the  purpose  of  making  moisture  determinations.  It  was 


1. 


---...:---- 
Mottle^,  yellow,  {Viable,  silty  clay  loarri';.-.- 


FIG.  6.  —  SKETCH  OF  SOIL  PROFILE  FOR  GRAY  SILT  LOAM  ON  TIGHT  CLAY,  SHOWING 

THE  COMPACTING  EFFECT  OF  EXPLODING  A  DYNAMITE  CHARGE  IN 

THE  PLASTIC  CLAY  STRATUM 

thought  that  if  any  of  these  tillage  treatments  increased  the  passage  of 
water  thru  the  tight  clay  stratum,  it  would  be  shown  in  the  moisture 
content  of  the  surface  and  subsurface  during  the  period  of  excess 
moisture  in  the  early  spring. 

TABLE  8.  —  PERCENTAGE  OF  MOISTURE  IN  SURFACE  AND  SUBSURFACE:   TOLEDO  FIELD* 


Plot. 


8 


Tillage  treatment Plowed  7  in.        Subsoiled         Deep  tilled        Dynamited 

Surface — 0-8  Inches 


April  30  

.  29 

4  + 

0.33 

79 

.3  +  0, 

74 

77 

?  + 

0.16 

29.4 

±  0.27 

May  7  

27 

5  + 

0.35 

77 

.8  ±  0. 

7S 

75 

8  + 

0.22 

29.8 

+  0.18 

May  15  

28 

7  + 

0.50 

78 

.2  +  0, 

75 

?S 

1  + 

0.25 

29.2 

+  0.21 

May  21  

28 

9  + 

0.28 

78 

.3  +  0. 

77 

76 

1  + 

0.20 

28.4 

+  0.28 

Seasonal  average  

28 

.5  ± 

0.19 

28 

.4  +  0, 

,12 

26 

.1  + 

0.10 

29.3 

+  0.12 

Subsurface — 8  Inches  to  the  Tight  Clay 


April  30  

.    25 

.0  ±  0, 

44 

22 

9  + 

0.34 

73 

8  + 

0.16 

24.2 

±  0.26 

May  7  

'  23 

.3  ±  0, 

40 

77 

0  t 

0.32 

22 

9  + 

0.20 

24.6 

±  0.23 

May  15  

.    .      24 

.1  ±  0, 

46 

'M 

1  + 

0.30 

71 

7  + 

0.18 

25.1 

+  0.29 

May  21  

26 

.3  ±  0, 

34 

7S 

7  ± 

0.41 

?<; 

5  ± 

0.27 

25.9 

+  0.18 

Seasonal  average  

24 

.9  +  0, 

.20 

23, 

.9  + 

0.17 

24, 

,o± 

0.10 

24.9 

+  0.12 

fourteen  samples  from  each  plot  on  each  date. 


1925~\  SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING  167 

It  will  be  noted  by  reference  to  Table  8  that  there  were  no  signifi- 
cant differences  in  1920  in  the  moisture  content  of  the  plots  which 
had  received  the  various  tillage  treatments  the  previous  fall  and  also 
in  the  fall  of  1915.  It  seems  apparent  that  none  of  the  tillage  treatments, 
subsoiling,  deep  tilling,  or  dynamiting,  had  any  effect  which  was  re- 
flected in  the  moisture  content  of  this  poorly  drained  prairie  soil. 

EXPERIMENT  AT  URBANA:    SOIL  VARYING  FROM  BROWN  SILT 
LOAM  TO  BLACK  CLAY  LOAM 

In  1915,  an  experiment  on  time  and  depth  of  plowing  was  started 
on  the  900  and  1000  series  of  the  University  South  Farm.  The  soil  on 
these  two  series  varies  from  Brown  Silt  Loam  to  Black  Clay  Loam, 
probably  corresponding  to  Muscatine  silt  loam  and  Clyde  clay  loam  as 
classified  by  the  Bureau  of  Soils  of  the  United  States  Department  of 
Agriculture.  A  four-year  rotation  of  corn,  corn,  oats,  and  sweet  clover 
occupies  these  two  series,  each  crop  being  grown  each  year. 

The  times  and  depths  of  the  various  plowing  operations  are  shown 
in  Table  9.  A  two-bottom  gang  was  used  for  the  3  to  4-inch  depth, 
and  the  7-inch  depth,  and  a  deep  tillage  machine  for  the  12  to  14-inch 
depth. 

Also  in  Table  9,  the  yields  of  first-year  corn  are  given  for  the  period 
of  the  experiment,  1915  to  1920,  and  the  yields  of  second-year  corn  for 
the  last  four  years. 

The  results  indicate  that,  in  so  far  as  the  yield  of  corn  is  concerned, 
there  is  no  choice  between  12  to  14-inch  fall  plowing,  7-inch  fall  plow- 
ing, and  7-inch  spring  plowing,  but  that  3  to  4-inch  spring  plowing  is 
apparently  too  shallow  for  the  best  growth  of  corn.  The  differences, 
however,  in  favor  of  the  deeper  plowing  as  compared  with  the  shallow, 
are  not  large  enough  to  be  at  all  conclusive.  The  consistent  character 
of  the  results  indicates  that  no  increases  in  yields  can  be  expected  on 
these  soil  types  following  plowing  to  a  depth  of  12  to  14  inches  with 
the  deep  tillage  machine. 

COOPERATIVE  EXPERIMENTS 
1912  Experiment 

Late  in  May,  1912,  two  one-half  acre  plots  were  plowed  6  to  7 
inches  deep  and  two  other  half-acre  plots  plowed  12  to  14  inches 
deep  on  a  farm  two  miles  south  of  Urbana,  on  soil  which  is  classified 
as  Brown  Silt  Loam.  Corn  was  planted  within  a  few  days  following 
the  plowing,  after  disking,  rolling,  and  harrowing.  The  crop  yields  are 
given  in  Table  10. 

This  experiment,  while  inconclusive  because  of  lack  of  replication 
and  also  because  but  one  year's  work  was  done,  indicates  that  plowing 
to  a  depth  of  12  to  14  inches  for  corn  a  few  days  before  planting  is 


168 


BULLETIN  No.  258 


[February, 


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SUBSOILING,  DEEP  TILLING,  AND  DYNAMITING 


169 


harmful  on  Brown  Silt  Loam.   There  is  reason  to  believe  it  would  be 
equally  harmful  on  any  soil. 


TABLE  10. — ACRE  YIELDS  OF  CORN  GROWN  IN  COOPERATIVE 
EXPERIMENT:   URBANA,  1912 


Tillage  treatment 

Individual  plots 

Average 

Plowed  6  to  7  inches  deep  

bu. 

67.7 

bu. 
66.3 

64.9 

Deep  tilled  12  to  14  inches  

63.3 

56.4 

59.5 

1913  Experiment 

In  the  late  fall  of  1912,  four  one-acre  plots  were  plowed  6  to  7 
inches  deep  and  four  other  one-acre  plots  plowed  12  to  14  inches  deep 
with  the  deep  tillage  machine.  The  next  spring  the  seed  bed  was  pre- 
pared and  the  corn  planted.  Table  11  gives  the  yields  secured. 


TABLE  11. — ACRE  YIELDS  OF  CORN  GROWN  IN  COOPERATIVE  EXPERIMENT: 
URBANA,  1913 


Tillage  treatment 

Individual  plots 

Average 

Plowed  6  to  7  inches  deep  

bu. 
49.1 

47.2 

bu. 
44.9  +  1.62 

40.7 
42.6 

Deep  tilled  12  to  14  inches 

47.6 
43.7 

45.9  +  0.94 

44.3 
48.2 

It  will  be  noted  that  the  difference  in  the  average  yields  is  so  small 
as  entirely  to  lack  significance,  and  also  that  there  is  considerable  dif- 
ference shown  in  the  yields  of  individual  plots  which  received  the  same 
tillage  treatment.  This  fact  emphasizes  the  necessity  of  having  a  suffi- 
cient number  of  plots  in  any  work  of  this  sort  to  give  a  reasonably  re- 
liable average.  By  proper  selection  these  figures  could  be  used  to  prove 
either  that  ordinary  plowing  is  superior  or  that  deep  tilling  is  superior, 
when,  as  a  matter  of  fact,  there  is  no  significant  difference  shown  be- 
tween the  two  when  measured  in  terms  of  the  corn  crop. 


170  BULLETIN  No.  258 

THE  COST  CONSIDERATION 

The  merits  of  any  tillage  practice  are  determined  by  the  net  re- 
turns resulting  from  that  particular  practice.  It  costs  at  least  twice  as 
much  to  subsoil  a  field  as  it  does  to  plow  it  at  an  ordinary  depth. 
Probably  a  fair  statement  is  that  when  it  costs  $2.50  an  acre  to  plow 
7  inches  deep,  it  will  cost  $5  an  acre  to  subsoil,  and  $1  an  acre 
to  deep  till.  It  was  found  at  this  Station  that  it  takes  four  horses  to 
pull  a  subsoil  plow  and  six  horses  to  pull  the  deep  tillage  machine.  At 
Toledo,  a  two-plow  tractor  was  used  for  two  years  to  pull  the  deep 
tillage  machine,  and  it  was  overloaded. 

The  cost  of  dynamiting  varies  considerably  because  of  differences 
in  the  costs  of  material  and  labor,  but  it  is  always  high.  If  the  charges 
are  placed  at  intervals  of  one  rod  each  way,  and  one-third  stick  of  20- 
percent  dynamite  is  used  for  each  shot,  the  cost,  including  labor,  will 
range  from  $20  to  $25  an  acre,  when  dynamite  costs  30  cents  a  pound. 
It  is  apparent  that  very  large  increases  in  yield  would  have  to  follow 
the  dynamite  treatment  to  justify  its  use  for  general  farm  crops. 

ACKNOWLEDGMENT 

The  experimental  work  described  in  this  bulletin  has  involved  the  cooperation  of 
many  persons.  Special  acknowledgment  is  hereby  made  to  the  late  Professor  J.  G. 
Mosier,  and  to  Professor  A.  F.  Gustafson  and  Mr.  F.  A.  Fisher,  former  members  of 
the  Agronomy  Department. 


UNIVERSITY  OF  ILLINOIS-URBANA 


